1. Field of the Invention
This invention relates generally to dental implants, and is more particularly concerned with a drivable implant having torque resisting means.
2. Discussion of the Prior Art
When one or more teeth are to be replaced, it is a common practice to anchor the tooth or teeth prostheses to adjacent teeth. As long as the adjacent teeth are well seated in and secured by bone, the use of adjacent teeth to anchor a prosthesis works quite well. There are, however, times when the adjacent teeth are not sufficiently secure to endure the additional stress encountered in anchoring a prosthesis. In such events, the common practice is to install an implant having a post for securing the prosthesis. The implant is installed by drilling a hole into the bone, and inserting the implant into the bone. A post is then connected to the implant, and the prosthesis is attached to the post, usually by means of a threaded screw. The prosthesis can be installed and removed as desired, and this is done primarily during the fitting stages.
The prior art implants have taken two different forms. In one form, the implant includes a generally straight shank that is driven into the hole in the bone, by tapping with a mallet or the like. This driven implant has the advantage that the implant is quickly placed and is relatively nontraumatic to the bone. The disadvantages of the driven type implant are the fact that only frictional force secures the implant to the bone at the initial installation; and, the driven implant has minimal surface for subsequent tissue attachment. The advantages of the screw-in implant are that the implant is literally screwed into the bone, cutting its own threads in the process, so the screwed-in implant is very secure mechanically on initial installation. Further, the screwed-in implant has a very large surface area because of the threads, and this large surface area promotes attachment of tissue. The primary disadvantage of the screw-in implant is the trauma to the bone caused by the stresses of threading the implant into the drilled hole.
A further difficulty with both the above mentioned types of implants is the likelihood that the implant will be broken loose from its attachment during manipulation of the screw that holds the prosthesis. The driven-in implant has no mechanical means to prevent rotation of the implant, relying only on frictional force and tissue attachment. Both of these can be relatively easily overcome in attempting to remove a screw, especially if the screw has been in place for some time. The screwed-in implant has threads, and will also have some tissue attachment; but, attempting to remove a screw holding a prosthesis can unscrew the screwed-in implant. In either case, it will be understood by those skilled in the art that, once the implant has been broken loose from the tissue attachment, the implant must be removed and replaced.